add gulpfile.js and dependencies

[tapmorales]

npm-scripts start and build runs gulp tasks.

$ npm start just execute browserSync and serve the statik folder
$ npm run build executes more tasks:

• minify vendor.js into vendor.min.js
• minify app.js into app.min.js
• concat all .css files into main.min.css
• replace .css and .js above into index.html